There are many types of flat panel displays that have been and are currently being developed. One popular type of flat panel display is a liquid crystal display (LCD). LCDs generally perform well, but have somewhat narrow viewing angles, relatively slow signal response times, and require background lighting. Consequently, LCDs are not at their best for high-speed image animation and consume additional energy powering the background lighting. In addition, large LCDs are difficult to produce.
Organic light emitting diode (OLED) displays have been developed to address the disadvantages of LCDs. Unlike LCDs, which modulate light generated by their background lighting systems, OLED displays emit light via an array of OLED-based pixels.
FIGS. 1A and 1B respectively illustrate conventional bottom and top emission OLED pixel structures 120, 120′. The bottom emission OLED pixel structure 120 shown in FIG. 1A, is constructed on a transparent substrate 100 and includes: a bottom, transparent anode 130 disposed on the substrate 100; an organic light-emitting layer 140 containing an organic light-emitting material disposed on the anode 130; and a top, metal electrode 150 disposed on the organic light-emitting layer 140. Light is emitted from the bottom of the OLED pixel structure 120 by the light-emitting layer when an electric current passes between the anode 130 and the metal electrode 150.
The top emission OLED pixel structure 120′ shown in FIG. 1B, is constructed on a transparent substrate 100 and includes: a bottom, metal electrode 150′ disposed on the substrate 100; an organic light-emitting layer 140 containing an organic light-emitting material disposed on the metal electrode 150′; and a top, transparent cathode 135 disposed on the organic light-emitting layer 140. Light is emitted from the top of the OLED pixel structure 120′ by the light-emitting layer 140 when an electric current passes between the metal electrode 150′ and the cathode 135.
Although conventional bottom and top emission OLED pixel structures are satisfactory for OLED display applications that only require images to be displayed on one side of the display, there are potential OLED display applications that require images to be displayed on both sides of the display. Such a two-sided OLED display would require an OLED pixel structure that emits light from the top and the bottom.
Accordingly, a need exists for an OLED pixel structure that is capable of emitting light from the top and bottom thereof.